The production and handling of petroleum products often produces mixtures of product and water containing large amounts of dissolved or entrained hydrocarbons. For example, water removed from static separator tanks employed to separate oil from mixtures of oil and water can contain such high levels of hydrocarbons that, if discarded, it would be considered a hazardous waste, and could not be disposed of without further treatment. Further, if discarded, the dissolved or entrained petroleum is lost.
The treatment of such water can be quite expensive. When treated off-site, the required hauling and treatment process is costly. When treated on-site, the cost of hauling is eliminated, but the installation and operation of separate treatment units fed from holding tanks can also be very costly. In either case valuable hydrocarbon compounds in the water are destroyed by the treatment process.
Treatment processes have been suggested which will separate hydrocarbons from water. One example is disclosed in U.S. Pat. No. 4,564,447, wherein contaminated water is caused to flow in a shallow stream over perforated pipes through which air is bubbled. By this means, the air entrains and removes the contaminating dissolved solvent. Another example is disclosed in U.S. Pat. No. 4,892,664, wherein contaminated water is pumped from a well to the top of a packed column. While the water travels down the column, air is blown up through it, stripping hydrocarbons from the water.
As is obvious from these representative processes, they require considerable hardware and constant monitoring to ensure that operating conditions are within the proper parameters. Moreover, it is difficult to ascertain whether the treatment process adequately reduces the amount of hydrocarbons in all the water flowing through the system. This is because periodic samplings of the effluent merely reflect the condition of that portion of the flowing treated water at the time the sample was collected. They do not provide a precise reading of the amount of contaminants present in all of the water flowing through the process apparatus. Further, the processes require provisions for a holding tank to maintain constant liquid flow and/or a recovery tank for receiving the treated water, which further contributes to the cost of the installation.
It would be desirable to be able to treat water containing hydrocarbons in a simpler, yet effective way, so as to not only remove and recover hydrocarbons to a point where the remaining water is at an acceptable level, but to do so in a manner which assures that the entire output of the process is adequately clean. It would also be desirable for such a process to be relatively inexpensive and simple to operate.